Thousands of mourners began paying homage on Saturday to Italian fashion giant Giorgio Armani, following his death aged 91.

The designer died on Thursday after months of fragile health and will be laid to rest at a private funeral on Monday in Milan.

But members of the public are able to pay their respects this weekend, with his coffin laid out for public viewing at the Teatro Armani in the northern Italian city.

Hundreds of people were already queuing when the doors opened at at 9 am, led by a large group of Armani group staff, all in black mourning wear and black sunglasses.

The wooden coffin was laid in a darkened room, white flowers laid on top, and surrounded by white paper lanterns.

"It's so emotional," said Silvia Albonetti, an Emporio Armani saleswoman. "He was an incredible man... sometimes rude, but human."

"Every fashion show he was pure magic. No one has managed to make women stand out like he did. He will be missed," said fashion student Pietro Angeleri.

King of a luxury lifestyle empire worth billions of euros, Armani dressed Hollywood actors, pop stars and royals in understated but exquisitely tailored creations.

His death came just weeks before celebrations to mark the 50th anniversary of his fashion house at Milan Fashion Week.

The city, which adopted him as its own, has declared the day of his funeral a day of mourning.

Armani had no children, and his death leaves a question mark over the future of his empire.

His nieces Roberta and Silvana Armani work for the group, while his nephew Andrea Camerana is a board member.

In their statement marking his death, his family and employees committed "to protecting what he built and to carrying his company forward in his memory". (AFP)